1. Field of the Invention
The present invention relates to a method of maintaining freshness and quality of perishable foodstuffs, by preventing rot by controlling bacteria sticking to food and sterilizing food, such as fresh meat, fish, vegetable, fruit, egg, and processed food such as ham and sausage.
2. Brief Description of the Prior Art
Among methods for keeping freshness or quality of food hitherto, various methods using isothiocyanic ester which is a principal ingredient of wasabi have been proposed.
Methods for controlling bacteria sticking to food and sterilizing food by keeping the surface of food in direct contact with wasabi solution are known, for example, a method of preventing formation of fungi by immersing fruit or vegetable in a dispersed aqueous solution of wasabi without putting in a refrigerator (Japanese Laid-open Patent Hei. 2-79933), and a method of preventing formation of fungi by spraying a dispersed ethanol solution of wasabi directly to food. (Japanese Laid-open Patent Hei. 1-31109).
Also known is a method of controlling and killing bacteria in the entire atmosphere in an enclosed space, such as a method of sterilizing the enclosed space such as factory, warehouse and hold of a ship by using vapor of isothiocyanic ester (Japanese Laid-open Patent Hei. 3-101604).
In these prior arts, however, the following inconveniences are caused.
That is, isothiocyanic ester, the principle ingredient of wasabi, is a liquid not soluble in water, and when it is dispersed in water, it becomes unstable and generates so-called wasabi gas. Therefore, when immersing fruit or vegetable in this aqueous solution, it must be used shortly after preparing the aqueous solution, and when left over, the effect is lost in the course of time. On the other hand, when ethanol is used as the solvent, since the isothiocyanic ester is dissolved, the stability is increased, but since the isothiocyanic ester is enveloped in the solution, the part of the food not contacting with the solution lacks in the fungistatic and fungicidic effect. It is hence necessary to spray uniformly on the whole surface of the food, which is bothering. Or, by using an ethanol aqueous solution mixing ethanol and water as the solvent, it may be considered to obtain a stable wasabi solution generating wasabi gas in good balance, but since water is contained, although the effect is extended, it must be used shortly after preparation.
Anyway, in these methods, by direct contact of wasabi solution with the surface of food, the fungistatic and fungicidic effects are obtained only on the surface of the food, and the entire atmosphere lacks the fungistatic and fungicidic effects, the effects fade away shortly unless the food is contained in a relatively small enclosed container to keep the atmospheric volume to contact with the food small. Besides, since the surface of the food is moistened, it cannot be applied to the food vulnerable to moisture.
By contrast, in the case of sterilizing by filing an enclosed space with vapor of isothiocyanic ester, the above inconveniences are eliminated, but it requires heating mechanism or cooling mechanism for generating vapor of isothiocyanic ester, and the facility is costly.
The invention is devised in the light of such background, and is intended to present a treating method for keeping food fresh capable of feeding wasabi gas easily and stably in an enclosed space.